In many industries, pipes or pipelines are utilized to transport fluid over distance. For example, in the oil and gas industry, there is a need to transport fluid over great distances and often over or through largely inaccessible terrain or deep water.
Of course, it will be recognized that it is important where a defect or penetration occurs in a pipe that the pipe is sealed to obviate or mitigate loss of fluid. Alternatively, it may be required to provide a sealed intervention into a pipe, for example, where a nozzle is to be added for the fitting of a branch or tee connection to a live pipeline containing fluid at pressure, typically termed “hot tapping.”
At present, one method of sealing a pipe is to use a saddle clamp to cover the defect or penetration in the pipe. The saddle typically seals on a pad or, alternatively, on a ring seal encircling the defect or penetration to prevent escape of fluid from the pipe. In such an arrangement, energization of the seal is attained by pre-loading the seal on installation of the clamp, the pre-load being of a force in excess of the load generated by internal pressure within the pipe during operation. In this way, the penetration or defect may be isolated to prevent escape of fluid from the pipe.
The use of a clamp arrangement such as that described above operates sufficiently well for low pressure systems. However, the pre-load necessary to maintain the required sealing force is significant in relatively high pressure systems. There is also a need for the load to be evenly distributed over the seal. This can be problematic where, for example, the clamp is fitted to a de-pressurized pipe, as the pre-load may be sufficient to deform the pipe resulting in further defects or deformation to the pipe. This is particularly prevalent where the pre-load is applied to a thin walled pipe with low internal pressure.
Furthermore, it is known that the internal pressure in a pipe produces a radial force which resists external forces applied to the pipe. Thus, where the internal pressure within the pipe increases, an extrusion gap can form in the seal resulting in a reduction in operational effectiveness or failure of the seal.